The invention relates to plasma-based, remote excitation sources for use with processing chambers, e.g. plasma processing chambers.
Plasma based, remote excitation sources or reactive species generators must often be able to handle high input powers and withstand high temperatures combined with a highly reactive chemical environment. For example, in a common application of a reactive species generator, NF.sub.3 gas flows into the generator and is broken down by the plasma. The resulting activated species flows out of the generator and into the semiconductor processing equipment where it is used for in-situ chamber cleaning, etching, photo resist stripping, or any of a number of other tasks. As an example of using the reactive species for in-situ chamber cleaning refer to U.S. Ser. No. 08/278,605, entitled "A Deposition Chamber Cleaning Technique Using a Remote Excitation Source" filed on Jul. 21, 1994, and incorporated herein by reference.
The extremely hostile environment to which such equipment is exposed can disable the plasma-based generator very quickly. For example, some generators that are commercially available use quartz tubes to contain the activated species. In those systems, the fluorine that is produced etches the tube quite quickly. Moreover, at high power levels (e.g. above 1 or 1.5 kW) the quartz will tend to break down. Thus, after using the generator only a few times or for a sustained period of operation, the wall of the tube will be become so thin that it will soon collapse under continued exposure to the high temperatures and the vacuums that prevail in such systems. Thus, very early in the life of the tube, it must be discarded and replaced with a new tube. Both the inconvenience and cost of having to repeatedly replace the quartz tube can be quite high.
Some existing plasma-based generators use ceramic tubes in place of the quartz tubes. Ceramic tubes are capable of holding up better than the quartz tubes in the chemically corrosive environments often encountered. But ceramic tubes are not a panacea. They typically have a relatively high thermal expansion coefficient as compared to quartz and other materials. Thus, repeated cycling between room temperature and the high processing temperatures that commonly occur in these systems produces large stresses within the ceramic tubes. These stresses eventually result in the tubes cracking and failing.
Unfortunately, the plasma tubes are not the only components that fail. Seals and O-rings which aid in maintaining a vacuum within the plasma tube also rapidly deteriorate and eventually fail when exposed to the high temperatures produced in such systems.